1. Field of the Invention
This invention is generally related to the detection of viral contaminants in ground and surface waters and, more particularly, to qualitative and quantitative testing systems for quick and accurate detection of viral contamination.
2. Description of the Prior Art
In 1914, the United States Public Health Service adopted the coliform group of bacteria (total and fecal) as the accepted indicator of fecal pollution of drinking water. Even though many bacteria included in the coliform group are not of fecal origin, research on microbial indicators supports the conclusion that the coliform standard is a satisfactory indicator of bacterial fecal contamination. However, there are serious concerns that the coliform group may not be a reliable indicator of viral fecal contamination. Many enteric viruses are more resistant than Escherichia coli to a variety of adverse environmental conditions and waste treatment processes, including chlorination, because of their acellular nature and highly resistant protein coat.
Viruses found in domestic sewage can pose a greater health problem for humans than bacteria because the dose required to cause sickness is much less than with bacteria. Documented waterborne outbreaks of viral disease have largely been limited to the agent of infectious hepatitis because of its characteristic symptomology. Other waterborne virus disease outbreaks have not been as easily recognized, and well documented outbreaks attributable to many specific enteric viruses are lacking.
There is presently no routine drinking water examination procedure for enteric viruses because of the cumbersome isolation techniques that include mammalian cell cultures, high costs of materials, and the need for skilled laboratory personnel experienced in enteric virus isolation and enumeration techniques.
There is a growing consensus among scientists that coliphages, which are viruses that infect E. coli, can be used as indicator organisms for the presence of human pathogenic viruses, much in the same way as coliforms are used to indicate the possible presence of bacterial pathogens. Coliphages are an extensive and diverse group of viruses that include medium and large DNA bacteriophages, small genome DNA viruses, and single and double stranded DNA and RNA viruses. The most frequently reported or routinely isolated are the medium and large DNA coliphages such as T-phages, phage lambda, P2-4 phages, and the lipid containing phages. Many of the DNA coliphages are of roughly the same size and molecular weight as the more common enteric viruses and can be used as models for enteric virus survival. Reports suggest that coliphages and enteric viruses are removed at comparable rates during treatment processes, that certain coliphages are at least as resistant to environmental stresses and to chlorination as enteric viruses, and that coliphages exhibit a seasonal variation similar to that of enteric viruses. Currently, coliphage detection as an indicator of the sanitary quality of water has been proposed by the American Public Health Association and is under serious consideration (see, Standard Methods for the Examination of Water and Wastewater, 1989, 17th ed., L. S. Clesceri et al. (eds.), Sections 9-36 & 9-37, Amer. Public Health Assoc., Wash. D.C.).
The method proposed by the American Public Health Association (APHA) for the detection and enumeration of coliphages from ground and surface water is a single-agar-layer plaque technique which is analogous to colony counting in bacteria. It is recommended that E. coli C (ATCC 13706) be used as the host (because it is a restriction-less strain which prevents infecting phage DNA degradation), and that 2,3,5-triphenyl tetrazolium chloride (TPTZ) be added to the agar as an oxidation-reduction agent to provide a contrast to detect cleared zones (plaques). In the APHA method, as non-infected E. coli cells grow, the TPTZ is reduced and lends a pale pink color to the agar while plaques (infected and killed E. coli) remain colorless. Plaques are then counted to provide enumeration of the number of coliphages in the original water sample.